Put the butter and peanut butter in a medium to large bowl. Cover with a paper plate. Plastic wrap may alternatively be used, however, I wasn’t so sure about plastic in the microwave. Microwave on high for 2 minutes. Stir before microwaving on high for two more minutes. The mixture will be bubbling and incredibly hot, so use caution. Stir briefly before adding vanilla and confectioners’ sugar. Stir with a large spoon to incorporate all of the ingredients. The mixture will become difficult to stir and will lose its sheen. Once this has happened, scoop the mixture into a square 8 inch pan lined with parchment paper with a large overhang. Spread the mixture as evenly as possible in the pan. Fold excess parchment over the top of the fudge to cover it. Refrigerate until completely cooled, about 2 hours. Cut into 64 1 inch pieces, 8 cuts across the top, 8 cuts down the side. Fudge may be stored in an airtight container at room temperature for up to one week. Alternatively, fudge freezes incredibly well. To do so, wrap it in parchment and foil, place it in a freezer bag, and thaw at room temperature for several hours before enjoying.